1. Field of the Invention
The present invention relates to a buoy having excellent resistance against external pressure. More particularly, it relates to a buoy having a buoyant member formed from a high density polyethylene foam and exhibiting a reduced loss of the buoyancy during use.
2. Description of the Prior Art
Buoys comprising a low density polyethylene foam as the buoyant member and an outer skin covering the foam have heretofore been used for anchoring ships or as observation and marking buoys. Such buoys are used by floating them on the surface of the water. However, about 2/3 of the total volume is always submerged in water, and the submerged portion receives an external force from the water pressure. Accordingly, it is required that the buoys should float on the water surface while retaining a buoyancy capable of resisting the external pressure which the submerged portion receives during use.
In the conventional buoys, however, since a low density polyethylene foam in which a change of the volume by the external force is large is used as the buoyant members, and when the buoys receive the external force, the volume of the buoyant members is drastically reduced and the loss of the buoyancy is increased by reduction of the displacement. In an extreme case, there is no superfluous buoyancy and the buoys are entirely submerged in water.
In the conventional buoys, therefore, a structure having a large superfluous buoyancy should be adopted to cope with the reduction or the buoyancy by the external force, and therefore, the size of the buoys must be increased and the handling of the buoys becomes difficult.